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>Chapter 12. Backups</TD
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>12.1. On the importance of being backed up</A
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><P
> Your data is valuable.  It will cost you time and effort
	re-create it, and that costs money or at least personal grief
	and tears; sometimes it can't even be re-created, e.g., if it
	is the results of some experiments.  Since it is an investment,
	you should protect it and take steps to avoid losing it.  </P
><P
> There are basically four reasons why you might lose data:
	hardware failures, software bugs, human action, or natural
	disasters.
	
		<A
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>[1]</A
>
		
	Although modern hardware tends to be quite reliable, it can
	still break seemingly spontaneously.  The most critical piece
	of hardware for storing data is the hard disk, which relies on
	tiny magnetic fields remaining intact in a world filled with
	electromagnetic noise.	Modern software doesn't even tend to
	be reliable; a rock solid program is an exception, not a rule.
	Humans are quite unreliable, they will either make a mistake, or
	they will be malicious and destroy data on purpose.  Nature might
	not be evil, but it can wreak havoc even when being good.  All in
	all, it is a small miracle that anything works at all.	</P
><P
> Backups are a way to protect the investment in data.
	By having several copies of the data, it does not matter as much
	if one is destroyed (the cost is only that of the restoration
	of the lost data from the backup).  </P
><P
> It is important to do backups properly.	Like everything
	else that is related to the physical world, backups will fail
	sooner or later.  Part of doing backups well is to make sure
	they work; you don't want to notice that your backups didn't work.
	
		<A
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>
		
	Adding insult to injury, you might have a bad crash just as
	you're making the backup; if you have only one backup medium,
	it might destroyed as well, leaving you with the smoking ashes
	of hard work.
	
		<A
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>[3]</A
>
		
	Or you might notice, when trying to restore, that you forgot to
	back up something important, like the user database on a 15000
	user site.  Best of all, all your backups might be working
	perfectly, but the last known tape drive reading the kind of
	tapes you used was the one that now has a bucketful of water
	in it.	</P
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> When it comes to backups, paranoia is in the job
	description.  </P
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>[1]</A
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>The fifth reason is ``something
		else''.</P
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>[2]</A
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><P
>Don't laugh.  This has happened to
		several people.</P
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><A
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>[3]</A
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>Been there, done that...</P
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